Existing data suggest that the invertebrate species Hydra vulgaris does not show increased mortality with age. Interestingly, a closely related species, H. oligactis, shows increased mortality and physiological deterioration following induction of sexual reproduction. The long- term goal of this project is to identify the causes of this striking difference in longevity. Aspects of the biology of the Hydra vulgaris and Hydra oligactis suggest that some mechanisms affecting lifespan in other animals may contribute to the difference between the two species. Hydra oligactis induced to reproduce sexually form large numbers of gametes well before the onset of increased mortality. In addition, Hydra oligactis are less tolerant than Hydra vulgaris of environmental stresses such as thermal stress, and they fail to produce detectable levels of new proteins in response to heat shock conditions. Working with animals treated to eliminate the stem cells which produce gametes, we will investigate the possibility that, as in Caenorhabditis elegans and Drosophila melanogaster, germ cells in H. oligactis can reduce lifespan. By examining gene expression and producing transgenic animals which inducibly overexpress genes of interest, we will investigate the roles of genes involved in the heat shock response and the role of the transcription factor FoxO in H. vulgaris and in H. oligactis before and after induction of sexual reproduction and senescence. PUBLIC HEALTH RELEVANCE: The proposed project will investigate the differences in regulation of lifespan in two closely related species, Hydra vulgaris and Hydra oligactis. It will focus on possible roles of signals from the germline, proteins involved in the heat shock response, and the transcription factor FoxO. As amply demonstrated by information gained from Caenorhabditis elegans and Drosophila melanogaster, work on the mechanisms of longevity control in invertebrate species can provide insight into the causes of human aging-related disease. Hydra have the potential to provide different types of information than these two well-developed invertebrate models, however, since in contrast to both species they are relatively long-lived.